The present invention relates generally to magnetoresistive heads used for magnetic storage, such as a magnetic disc drive and a magnetic tape.
Along with recent smaller and higher density productions of magnetic disc drives decrease a floating amount of a head slider, and demand contact recording/reproducing that has an extremely low floating height or requires a slider to contact a record carrier.
A conventional magnetic inductive head deteriorates reproduction output as the circumferential speed, which is a relative speed between a head and a medium, decreases in a small magnetic disc. Magnetoresistive (“MR”) heads, which provide a reproduction output that does not depend upon the circumferential speed and therefore maintain a large output even for the low circumferential speed, are vigorously developed and used mainly for magnetic heads. More recently, magnetic heads that utilize a Giant Magnetoresistive (“GMR”) effect come into the market.
The high-recording density of a magnetic disc drive reduces a recording area per bit, and weakens a generated magnetic field. Therefore, MR sensors and heads are demanded which can be applied to a finer magnetic field range and detect changes of a weak external magnetic field.
At present, spin-valve MR sensors that utilize a spin-valve GMR effect have been frequently used for magnetic heads. The spin-valve MR sensors vary a magnetization direction of a free ferromagnetic layer (or a free layer) according to a signal magnetic field from a record carrier, and changes of a relative angle to a magnetization direction of a pinned ferromagnetic layer (or a pinned layer) vary the resistance of the MR sensor.
A general design that attempts to apply this MR sensor to a magnetic head fixes the magnetization direction of the pinned layer onto a height direction of the MR device, and directs, in a device width direction orthogonal to the pinned layer, the magnetization direction of the free layer when no external magnetic field is applied.
This configuration can linearly increase and decrease the resistance of MR sensor according to whether the signal magnetic field direction from the magnetic record carrier is parallel to or antiparallel to the magnetization direction of the pinned layer. Such a linear resistance variance facilitates signal processing of the magnetic disc drive.
The conventional MR sensor applies the sense current parallel to a coating surface, and reads resistance changes that rely on the external magnetic field. This Current in Plane (“CIP”) configuration that applies the current parallel to GMR coating surface lowers an output as the sensing area that is defined by a pair of electrodes reduces. The CIP spin-valve MR sensor needs an insulating coating between the GMR coating and upper/lower magnetic shields.
In other words, a distance between the magnetic shields is equal to a sum of GMR coating thickness and insulating coating thickness times 2. Since the current insulating coating thickness has a lower limit of about 20 nm, a distance between the magnetic shields is equal to a sum of the GMR coating thickness and about 40 nm.
As the recording bit becomes shorter on the record carrier, the current CIP spin-valve MR sensors cannot meet a demand for the distance between the magnetic shields of 40 nm or smaller.
Proposed post spin-valve GMRs as one solution for this problem are a Current Perpendicular to Plane (“CPP”)-GMR configuration that applies the current perpendicular to the GMR coating surface, and a tunnel MR (“TMR”).
TMR is a configuration that holds a thin insulating layer between two ferromagnetic layers, and varies the tunnel current amount that flows through the insulating layer according to the magnetization directions of the two ferromagnetic layers. TMR exhibits such large resistance variance and good sensitivity that it is one of promising post spin-valve GMRs.
CPP-GMR characteristically provides a large output as the sectional area of a portion reduces, through which the sense current of the GMR coating flows. This feature is a great advantage over CIP-GMR.
Since the current flows from one ferromagnetic layer to the other ferromagnetic layer across the insulating layer in TMR, TMR can be regarded as a kind of CPP structure and has the above advantage.
Since the high-recording density of a magnetic disc drive promotes fine processing of a MR coating and results in reading of adjacent tracks during reproducing, a known structure provides a pair of magnetic shields at both sides of the MR coating in the track width direction. The MR head that utilizes the MR coating disadvantageously generates Barkhausen noises and greatly fluctuates reproduction outputs when the MR coating does not have a single magnetization.
Therefore, a magnetization control coating is provided to control the magnetization of the MR coating. A pair of magnetization control coatings are provided at both sides of the MR coating in the track width direction, and each include a high coercive force coating, typically made of CoPt, etc., or a layered coating that has an antiferromagnetic coating and a ferromagnetic coating, typically made of PdPtMn, etc. An alternative structure of the magnetization control coating layers an antiferromagnetic coating on a MR coating so as to form the magnetization control coating.
However, the magnetization control using the antiferromagnetic layer layered on the MR coating needs to make orthogonal to each other the pinning directions between the antiferromagnetic coating used for the MR coating and the antiferromagnetic coating used for the magnetization control, and is problematic in that the coating development is difficult. In addition, since the antiferromagnetic coating is layered on the MR coating, it is difficult to reduce a distance between the magnetic shields.
Moreover, when the magnetization control coatings, such as a high coercive force coating, are provided at both sides of the MR coating in the track width direction, the magnetization control coating should be located close to the MR coating. Therefore, it is very difficult to stably manufacture the magnetization control coating with good yield and to stably obtain the effect.
When the magnetic shields are provided at both sides of the MR coating in the track width direction for the high recording density, the magnetization control coatings cannot be provided at both sides of the MR coating in the track width direction.